Thousands of active black holes discovered where it was believed they couldn't exist

Black holes are among the most mysterious objects in the universe. Their immense gravitational pull can warp space and time, yet they remain invisible unless they interact with their surroundings.

Understanding black holes is crucial to deciphering the history of the cosmos. Scientists know that supermassive black holes sit at the centers of large galaxies, including the Milky Way.

However, much remains unknown about black holes in smaller galaxies.

Using early data from the Dark Energy Spectroscopic Instrument (DESI), researchers have uncovered an extraordinary population of black holes hiding in dwarf galaxies.

This discovery includes the largest-ever sample of dwarf galaxies with actively feeding black holes.

The study also presents the most extensive collection of intermediate-mass black hole candidates. These findings push the boundaries of astrophysics and open new avenues for exploring galaxy formation and evolution.

Mapping the Universe

DESI is one of the most advanced instruments in modern astronomy. It can capture light from 5,000 galaxies at once, allowing scientists to collect vast amounts of data efficiently.

The instrument operates on the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory in Arizona.

The project is funded by the Department of Energy (DOE) and the National Science Foundation (NSF), with contributions from international partners.

The DESI survey is in its fourth year and aims to observe 40 million galaxies and quasars. This ambitious project involves over 900 scientists from 70 institutions worldwide.

DESI’s precision and large-scale capabilities make it a crucial tool in identifying hidden black holes across the universe.

Hunting for black holes in dwarf galaxies

Dwarf galaxies are small, faint, and contain fewer stars than massive galaxies. They are difficult to study because their black holes are not as prominent.

In large galaxies, astronomers can detect black holes by observing the movement of stars and gas around them. However, dwarf galaxies require a different approach.

One way to find black holes in these galaxies is by identifying active galactic nuclei (AGN). When a black hole consumes surrounding material, it releases a massive amount of energy, making it easier to detect.

This energy illuminates the surrounding region, acting as a signal for scientists.

“When a black hole at the center of a galaxy starts feeding, it unleashes a tremendous amount of energy into its surroundings, transforming into what we call an active galactic nucleus,” says Ragadeepika Pucha, a postdoctoral researcher at the University of Utah.

The team identified 2,500 dwarf galaxies hosting AGN – the largest sample ever discovered. Previous studies estimated that only 0.5% of dwarf galaxies contained an AGN, but this new research suggests a much higher percentage.

These results indicate that many low-mass black holes have remained undetected until now.

Mystery of intermediate-mass black holes

Most known black holes are either stellar-mass or supermassive. Stellar-mass black holes form when massive stars collapse.

Supermassive black holes exist at the centers of large galaxies, weighing millions to billions of times the mass of the Sun. However, intermediate-mass black holes remain elusive.

Scientists believe these mid-sized black holes could be the remnants of the first black holes formed in the early universe.

They may also be the seeds that eventually grew into supermassive black holes. Despite their importance, only about 100-150 intermediate-mass black hole candidates had been identified before DESI’s survey.

In their search, researchers found 300 new intermediate-mass black hole candidates, the most extensive collection to date. This dataset provides a powerful tool for studying how these black holes form and evolve.

Advancements in black hole detection

Detecting black holes in dwarf galaxies requires high-precision instruments. DESI’s advanced design played a key role in this discovery.

The instrument uses small optical fibers to capture light from distant galaxies. This allows researchers to focus on the central regions of galaxies without interference from surrounding starlight.

“The technological design of DESI was important for this project, particularly its small fiber size, which allowed us to better zoom in on the center of galaxies and identify the subtle signatures of active black holes,” said Stephanie Juneau, associate astronomer at NSF NOIRLab.

Previous instruments had larger optical fibers that collected too much light from the outskirts of galaxies. This extra light diluted the signals scientists were searching for.

DESI’s small fibers provided a clearer view of black hole activity in dwarf galaxies, leading to a higher detection rate than previous surveys.

Unexpected findings and new questions

Scientists expected most black holes in dwarf galaxies to be intermediate-mass. However, the study revealed an unexpected result.

Of the 2,500 dwarf AGN candidates, only 70 overlapped with the 300 intermediate-mass black hole candidates.

This suggests that many of the detected black holes in dwarf galaxies may be more massive than previously thought.

The findings raise new questions about how black holes form and evolve in different types of galaxies. Do different black hole formation processes occur in dwarf and large galaxies? Are some intermediate-mass black holes growing more rapidly than expected?

“For example, is there any relationship between the mechanisms of black hole formation and the types of galaxies they inhabit?” Pucha said.

“Our wealth of new candidates will help us delve deeper into these mysteries, enriching our understanding of black holes and their pivotal role in galaxy evolution.”

Future of black hole research

DESI’s discoveries mark a turning point in the study of black holes. The new dataset will help scientists explore the early stages of black hole growth and their impact on galaxy evolution. As the DESI survey continues, researchers expect to uncover even more hidden black holes.

By studying these newly identified black holes, scientists hope to answer fundamental questions about the structure and history of the universe.

Future research will focus on confirming the nature of these candidates and examining how they interact with their host galaxies.

Black holes remain one of the greatest mysteries of astrophysics. Thanks to DESI, scientists now have a powerful tool to uncover their secrets, bringing us closer to understanding the forces that shape the cosmos.

The study is published in The Astrophysical Journal and arXiv.

Image Credit: NOIRLab/NSF/AURA/J. da Silva/M. Zamani

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